Seed-zone Water Research Articles

Tillage timing to improve soil water storage in Mediterranean long fallow

Creation of a dry soil mulch to maintain near-surface moisture in dry environments is an ancient practice that is still used in many regions of the world for timely establishment of crops after long fallow. Before availability of herbicides, the first tillage during fallow was timed to kill weeds, but now the optimum timing for tillage depends only on the interplay of evaporation and infiltration of rain. The goal is to maximize total root zone water storage and seed-zone water at seeding time. Our objective was to measure the effect of delaying soil mulch creation progressively later in the spring and summer on weed-free fallow for winter wheat (Triticum aestivum L.) in the Mediterranean inland Pacific Northwest drylands of the United States. Over a period of six years and a total of 12 site-years, four to seven tillage timings were compared to an untilled treatment. Soil water was measured at seeding time in the seed zone and total root zone. Seed-zone water and total stored water produced by different tillage timings was surprisingly constant, with few statistically significant or substantial differences. On average, only 2% of stored water was lost in the top 1.0 m of soil over 80 days during the hot, dry period towards the end of fallow. Responses to late spring rain could be seen, and tillage near the end of June (early summer) often produced maximum soil water content.

Wheat stubble height effects on soil water capture and retention during long fallow

A 4-yr study was conducted in a dry Mediterranean region of the Inland Pacific Northwest USA (PNW) to measure winter wheat (WW) (Triticum aestivum L.) stubble height and orientation effects on overwinter precipitation capture in the soil and subsequent water retention during ensuing dry summer months. The stubble was left standing and undisturbed during the 13-mo fallow periods. Stubble-height treatments were:(i) short (8 cm), (ii) medium (25 cm), and (iii) tall (75 cm). An additional treatment: (iv) mow tall stubble in mid-June, was included in the final two years. Soil water measurements were obtained at the beginning, middle, and end of fallow in 15-cm increments to a depth of 180 cm. Additionally, seed-zone water content was measured at the end of fallow in 2-cm increments to a depth of 26 cm. Near-surface soil temperature was measured from June-August. On average, tall- and medium-height stubble captured 34 and 32 mm (p = 0.002) more overwinter precipitation, respectively, than short stubble and these values were particularly pronounced (91 and 79 mm greater than short stubble) during a winter of heavy snow drifting. However, from mid-April until late August, the tall stubble lost an average of 91 mm of soil water compared to 70 and 59 mm in the medium and short stubble treatments (p < 0.001). Mowing tall stubble in mid-June before the hot, dry summer did not improved water retention. Continuous soil temperatures at 3, 7, 15, 25, and 40-cm depths measured electronically from June-August were coolest with the short, mowed, medium, and tall stubble, respectively, with frequent significant differences of > 1 °C among treatments. We speculate that soil in the tall treatment was warmest and lost the most over-summer water because all stubble was standing and offered less soil shading than the other treatments. At the end of fallow, medium and tall stubble averaged 14 and 8 mm greater soil water, respectively, than the short treatment (p = 0.027). Short stubble was a disadvantage for overwinter precipitation capture but was equal or better than the other treatments for retaining soil water from April to late August; presumably because this treatment had the most residue lying flat on the soil surface for shading. These findings offer opportunity to improve current models for soil water dynamics during fallow by incorporating stubble height. For combined soil water retention and farm management factors, medium-height WW stubble is the best fallow option for farmers in the PNW drylands.

Seven rainfed wheat rotation systems in a drought-prone Mediterranean climate

Increasing cropping intensity and use of no-till fallow (NTF) has been successful in many rainfed Mediterranean agricultural regions around the world, including of the Inland US Pacific Northwest (PNW) where annual precipitation exceeds 290mm. However, in the low-precipitation (<290mm annual) region east-central Washington and north-central Oregon, these practices have not been widely adopted and a 2-year winter wheat (Triticum aestivum L.)-tilled summer fallow rotation is practiced by the vast majority of farmers. The objective here was to evaluate the productivity of seven wheat rotation systems that reduce or eliminate tillage and increase cropping intensity in a 6-year study at Lind, WA. The study included: (i) soft white, hard red, and hard white market classes of wheat; (ii) both NTF and undercutter conservation-tillage summer fallow (UTF), and; (iii) continuous annual no-till cropping of wheat. Crop-year (September 1–August 31) precipitation over the six years averaged just 217mm. Across years, market class, and rotation system, spring wheat (SW) grain yield was only 33% of winter wheat (WW) after UTF. Thus, although only one crop was produced every other year with WW-UTF, this system had water use efficiency (WUE) of 5.5 grain/mm precipitation versus as low as 3.0kg grain/mm precipitation for SW with no preceding fallow year. Possible mechanisms for differences in grain yield and WUE among rotations were: (i) Russian thistle (Salsola tragus L.) weed infestation was at least eleven times greater in the various SW systems and much greater still with WW after SW with no fallow year compared to in WW after NTF and UTF, and; (ii) precipitation storage efficiency (PSE) in the 180cm soil profile during fallow for NTF-WW-SW was only 30% compared to 39 and 42% for the UTF-WW-SW and UTF-WW treatments, respectively. Critically, the seed zone of NTF was too dry for early planting of WW in most years whereas adequate seed-zone water was present every year in the UTF systems. Primarily due to late planting necessitated from lack of seed-zone water, grain yield of WW after NTF was reduced 35% compared to WW after UTF. Optimum grain yields and soil conservation are both required for sustainable agriculture, and WW with the UTF method was the clear winner of systems evaluated in this study.

Critical water potentials for germination of wheat cultivars in the dryland Northwest USA

AbstractLow soil water potential limits or prevents germination and emergence of rainfed winter wheat (Triticum aestivum L.). This phenomenon is particularly pronounced in the winter wheat–summer fallow region of the US Inland Pacific Northwest, where wheat is routinely sown deep to reach moisture with 12–15 cm of soil covering the seed. Wide differences in seedling emergence among winter wheat cultivars have been reported, but few previous experiments have examined germination differences among cultivars as a function of water potential. The objective of our laboratory study was to quantify seed germination of five commonly sown winter wheat cultivars (Moro, Xerpha, Eltan, Buchanan and Finley) at seven water potentials, ranging from 0 to − 1.5 MPa. Germination was measured as a function of time for a period of 30 d. At higher water potentials (0 to − 0.5 MPa), all cultivars had germination of more than 90%. At the lowest water potentials ( − 1.0 to − 1.25 MPa), however, Moro consistently exceeded the other cultivars for speed and extent of germination, with total germination of 74% at − 1.0 MPa and 43% at − 1.25 MPa. Since its release in 1966, Moro has been sown by farmers when seed-zone water conditions are marginal. Scientists have long known that coleoptile length is an important factor controlling winter wheat seedling emergence from deep sowing depths. In addition to having a long coleoptile, our data suggest that Moro's known excellent emergence ability from deep sowing depths in dry soils can also be attributed to the ability to germinate at lower water potentials than other cultivars.

Predicting seed-zone water content for summer fallow in the Inland Pacific Northwest, USA

The Horse Heaven Hills in south-central Washington contains the world's driest rainfed wheat ( Triticum aestivum L.) region. The climate is Mediterranean with average annual precipitation as low as 150 mm. The cropping system is winter wheat-summer fallow. Tillage is used in the spring of the 13-month fallow to establish a dry soil mulch to help retain seed-zone water to establish winter wheat planted deep into fallow in late August. However, the Horse Heaven Hills is often so dry that even tillage-based summer fallow (TF) cannot retain adequate seed-zone water, and farmers must then wait until the onset of rains in mid October or later for planting. In such dry years, farmers would be better off practicing no-till fallow (NTF) to protect the soil from wind erosion; but no predictive tools are available to assist in these decisions. The objectives of our study were (1) to predict seed-zone water contents and water potentials in late August or early September based on soil water content measured in early April and (2) to compare seed-zone water in TF and NTF. Experiments were conducted for 5 years at each of two sites. Soil water content was measured in both early April and late August. Soil properties and residue loads were characterized to calibrate the Simultaneous Heat and Water model (SHAW). Seed-zone water was simulated in late August based on measured soil water contents in early April and measured temperature and precipitation from April to August. The SHAW model correctly predicted seed-zone water content 80% of the time. The amount and timing of rainfall occurring in April, May, and June was the most important factor controlling the seed-zone water content in late August, suggesting that farmers should delay their decision on whether to practice TF or NTF until late in the spring.

Soil Water and Temperature in Chemical Versus Reduced-Tillage Fallow in a Mediterranean Climate

A 2-year rotation of winter wheat (Triticum aestivum L.)-summer fallow is a dominant cropping system in the dryland region of the Pacific Northwest United States. Traditional, tillage-based summer fallow relies on a soil mulch to disrupt capillary continuity to conserve seed-zone water for early establishment of winter wheat. However, tillage to create the soil mulch and to subsequently fertilize and control weeds often results in unacceptable levels of wind erosion due to the burial of crop residues and the exposure of fine soil particles. Chemical (no-till) fallow (CF) and reduced-tillage fallow (RT) are two alternatives for reducing wind erosion. Our objectives were: (i) to assess the effects of CF and RT on seed- and root-zone temperature and water regimes; and (ii) to test the Simultaneous Heat and Water (SHAW) model for simulating management effects on soil temperature and water. Weather data, soil temperature, and water content were monitored in paired CF and RT treatments during April 2003-March 2004. The RT treatment was observed to retain more seed-zone water over summer compared to CF, consistent with relevant literature for Mediterranean environments and of critical importance to farmers. During the wet winter, CF gained more water than RT because of later planting of winter wheat, and thus less water use. Observed soil temperatures were higher in the CF due to its lower dry soil albedo, higher bulk density and thermal diffusivity than in the RT. SHAW-simulated water contents followed the general trend of the field data, though it slightly under-predicted soil water content for CF and over-predicted for RT. SHAW under-predicted soil temperature during the dry summer and over-predicted for the wet (November-December) period yet the overall trend was properly described with differences between simulations and observations decreasing with soil depth. Overall, SHAW proved adequate in simulating seed-zone and whole-profile soil water and temperature, and therefore may serve as a useful modeling tool for tillage and residue management.

Fungicide Seed Treatment Effects on Emergence of Deeply Planted Winter Wheat

Winter wheat (Triticum aestivum L.) seed is often planted deeply (>3 in.) into stubble-mulch fallow in the semi-arid Pacific Northwest (PNW). Stand establishment is affected by factors that influence the rate of seed germination and coleoptile growth. Systemically translocated triazole and imidazole fungicide seed treatments were compared for effects on seedling emergence under conditions of deep seed placement and variable seed-zone moisture in stubble-mulch fallow systems. Fungicides included RTU Vitavax Thiram (carboxin [2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxathiin] + thiram [tetramethylthiuram disulfide]), Dividend (difenoconazole [1-(2-[4-(4-chlorophenoxy)-2-chlorophenyl]-4-methyl-1,3-dioxolan-2-yl-methyl)-1H-1,2,4-triazole]), Raxil Thiram (tebuconazole [α[2-(4-chlorophenyl)ethyl]-α-(1,1-dimethylethyl)-1H1,2,4-triazole-1-ethanol] + thiram), NuZone and Flo-Pro IMZ (imazalil [1-(2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl)-lH-imidazole]), and Apron (metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alanine methyl ester)]). Gaucho (imidacloprid [1 [(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazoli-diniminel), a seed-treatment insecticide, was applied in some experiments. Seven field and three greenhouse experiments were performed from 1993 to 1995. Emergence in the field tended to be superior for seed treated with Dividend, alone or mixed with Apron, in plantings made from 1- to 5-in. deep into soil with 5 to 17% seed-zone water content and at 71 to 80°F. RTU Vitavax Thiram had variable effects on seedling emergence. NuZone and Raxil Thiram, alone or mixed with Gaucho, generally delayed emergence when treated seed was planted at depths more than 2 in. In the greenhouse, treated seed was planted at 1-in. depth into moist (7, 10 or 15% w/w), warm (75°F) silt loam overlain by 4-in. of dry silt loam, simulating a planting at 5-in. depth into stubble-mulch fallow during September. Emergence of Dividend-treated seed at each soil moisture content was usually more rapid than for other treatments, including seed planted without fungicide treatment. This research demonstrated that emergence of winter wheat planted deeply into stubble-mulch fallow is often improved when seed is treated with Dividend compared with RTU Vitavax Thiram and, among the systemically translocated triazole fungicides, Dividend is a better choice than Raxil when planting depths exceed 2 in.

Soil physical constraints to establishment of mungbeans ( Vigna radiata L. Wilczek) in paddy rice ( Oryza sativa L.) soils

In several rice producing countries, production of upland crops, such as mungbeans ( Vigna radiata L. Wilczek), is an important means to save foreign exchange on food imports and to exploit the residual soil water following paddy rice ( Oryza sativa L.) harvest. Since the soil physical requirements for establishment and growth of upland crops are different from those for paddy rice, this study examined (1) soil physical properties that may limit mungbean emergence in rice soils, and (2) soil management techniques that will alleviate the soil physical constraints to mungbean establishment. Dry soil conditions and high soil resistance were the major soil physical constraints limiting mungbean seedling emergence in clay soils in a growth chamber experiment. Since seedzone water content is high after rice harvest, soil strength was viewed as the major constraint to mungbean emergence in paddy rice soils. This hypothesis was tested in a field experiment where tillage practices (moldboard plow, no-till), planting techniques (inverted-T, dibble, furrow), and delays to planting after rice harvest (1–3, 4–5, 7–8, 11–12, or 14–15 days after field drainage) were used to create varying soil strength conditions. The soil was Maahas silty clay (Vertic Tropaquept). Mungbean emergence and soil strength data showed that the maximum emergence corresponded to soil conditions where soil resistance to seedling emergence was lowest. There were few benefits from tillage on mungbean emergence. Inverted-T and furrow planting performed best in tilled and no-till plots, respectively. The optimum time for mungbean planting was from 1 to 8 days after field drainage for no-till, and from 3 to 5 days after field drainage for tilled soils.

Effect of management of a Himalayan Alfisol on water conservation for rainfed crops

Field experiments were conducted during 1989 and 1990 to study the effect of various soil management practices on water conservation during the two prime planting periods in the lower Himalayan region. Treatments studied were: zero tillage with weed control (ZT+W), zero tillage (ZT), fine tilth (FT), coarse tilth (CT), zero tillage with surface-applied lantana ( Lantana camara L.) mulch at 10 t ha −1 (ZT+M), fine tilth with surface-applied lantana mulch at 10 t ha −1 (FT+M), fine tilth with surface-applied farmyard manure mulch at 10 t ha −1 (FT+FYM) and fine tilth with FYM incorporated at 10 t ha −1 (FYM). The soils were Typic Hapludalfs with pH 5.8, organic carbon 6.6 g kg −1 and cation exchange capacity 12 cmol (P +) (100 g) −1. The lantana mulch application to fine tilth (FT+M) or zero tillage (ZT+M) maintained higher seed-zone water content and profile water storage as compared with all the other treatments. Highest water depletion was observed under ZT+W treatment. Seed germination is likely to occur only under FT+M and ZT+M during the two prime planting periods, if field capacity water content is considered to be limiting for seed germination. However, for the other treatments rainfall would invariably be required to increase the surface water content, to allow germination and early seedling establishment.

Fallow Tillage Effects on Evaporation and Seedzone Water Content in a Dry Summer Climate

AbstractEarly fall establishment of winter wheat is essential for high yields and erosion control following fallow in the Pacific Northwest, USA. Successful early stands require tillage management that minimizes water loss from the seedzone during the relatively dry summer. A numerical model was developed to investigate the dynamic aspects of heat and water flow in the upper soil layers with emphasis on effects of conventional tillage fallow and no‐till (chemical fallow) on these processes and ultimately the seedzone water content. After 15‐day simulations used to verify the model with measured values of meteorological variables and soil properties, predicted and measured water content distributions across the seedzone generally agreed within 0.01 kg/kg. Exclusion of thermally induced vapor flow from the model gave a higher predicted evaporative water loss and poorer agreement between measured and simulated soil water content distributions. The values for characterizing the atmospheric boundary layer resistance were also critical for correctly simulating soil temperature and water content profiles. Evaporative water loss for no‐till over a 90‐day simulation period using measured meteorological inputs was 70% higher than for conventional tillage, resulting in water contents in the seedzone that were too low for successful stand establishment under chemical fallow. Thus, for the climatic conditions and the soil studied here, some tillage may be necessary for retention of adequate seedzone water for early fall‐winter wheat establishment.